This invention relates to a water injection propulsion device and more particularly to an improved jet propulsion unit and control therefore for a watercraft.
Jet propulsion units are becoming a very popular form for propelling watercraft because of their numerous advantages over the more conventional propeller type drive. In order to further improve the performance of a jet propulsion unit, it has been proposed to provide a variable throat section in the jet propulsion unit. Normally, the effective cross sectional area of the discharge nozzle is varied so as to vary the thrust generated by the jet propulsion unit. At times, automatic controls have been proposed for so varying the effective area during running of the unit. However, the types of controls previously proposed have been responsive to the instantaneous condition rather than to changes in the operating condition of jet propulsion unit. Thus, these devices do not always provide optimum efficiency.
For example, the acceleration thrust of the jet propulsion unit can be significantly improved by varying the throat area of the discharge nozzle. With previously proposed devices and even those having automatic control, the area of the nozzle is varied in response to a given condition and hence the device does not anticipate the operator's desire.
It is, therefore, a principal object to this invention to provide an improved jet propulsion unit and control therefore wherein transient conditions are sensed and the jet propulsion unit has its effective area controlled in response to the rate of change of the condition.
As a specific example of a transient condition where it is desirable to anticipate the operator's desires, the acceleration thrust of a jet propulsion unit varies in response to the cross sectional area. If accelerating at a low rate of speed, it is desirable to gradually change the effective area of the jet propulsion unit. However, if rapid acceleration is being encountered, it is desirable to move the jet propulsion nozzle to its maximum effective area rapidly and then gradually reduce the opening to a somewhat more restricted area as the speed of the watercraft continues to increase.
It is, therefore, a still further object to this invention to provide an improved acceleration device for a jet propulsion unit and a method of operating the effective area of the jet propulsion unit in response to changes in rates of acceleration.